The present invention relates to self-healing composite materials.
Thermosetting polymers, used in a wide variety of applications ranging from microelectronics to composite airplane wings, are susceptible to damage in the form of cracking. Often these cracks form deep within the structure where detection is difficult and repair is virtually impossible. In fiber reinforced polymer composites, cracking in the form of fiber-matrix interfacial debonding, ply delamination, and simple matrix cracking leads to degradation. In microelectronics, polymer encapsulates and polymer matrix composite printed circuit boards suffer from similar forms of damage, but in addition to mechanical failure, cracks cause electrical failure of the component. Microcracking induced by thermal and mechanical fatigue is a longstanding problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Typically, previously reported methods of successful crack healing require some form of manual intervention.
A proposed method of self-healing is described in “Self-Healing Composites Using Embedded Microspheres” D. Jung et al. Composites and Functionally Graded Materials vol. MD-80, in Proceedings of the ASME International Mechanical Engineering Conference and Exposition, 265-275 (1997). The proposed method uses polyoxymethyleneurea (PMU) microspheres to store a crack filling agent to be released into the crack and rebond the crack faces. The repair mechanism uses naturally occurring functional sites in a polyester matrix network to trigger the repair action. Adding a reactive component to trigger the crack filler solidification was specifically investigated in the case of embedded epoxide components and embedded amine groups, and it was found that the amine groups did not retain sufficient activity and was determined to be not feasible. The PMU microcapsules used contained an epoxide monomer.